1. Field of the Invention
The present invention relates to a piezoelectric vibrator, a manufacturing method of a piezoelectric vibrator, an oscillator, an electronic device, and a radio-controlled timepiece.
2. Description of the Related Art
Recently, in a mobile phone or a portable information terminal device, as a timing source of a time source or a control signal, a reference signal source or the like, a piezoelectric vibrator which makes use of a piezoelectric vibrating piece made of a piezoelectric material such as crystal is used. As a piezoelectric vibrating piece, a tuning-fork-type piezoelectric vibrating piece having a pair of vibration arm portions is adopted.
As this kind of piezoelectric vibrator, an SMD (Surface Mount Device) piezoelectric vibrator is known.
As shown in FIG. 21 and FIG. 22, as an SMD piezoelectric vibrator 200, there has been proposed an SMD piezoelectric vibrator in which a package 209 is formed of a base substrate 201 and a lid substrate 202, and a piezoelectric vibrating piece 203 having a pair of vibration arm portions 204 is housed in a cavity C formed in the inside of the package 209. In this piezoelectric vibrating piece 203, weight metal films 211 are formed on distal end portions of the vibration arm portions 204 respectively for adjusting frequency of the piezoelectric vibrator 200, and excitation electrodes 212 which vibrate the pair of vibration arm portions 204 in the direction that the pair of vibration arm portions 204 approaches to each other or is separated from each other are formed on base end portions of the vibration arm portions 204 using a material which differs from a material of the weight metal films 211.
In general, it is desirable that an equivalent resistance value (effective resistance value: Re) of a piezoelectric vibrator is lowered as much as possible. The piezoelectric vibrator which has a low equivalent resistance value can vibrate piezoelectric vibrating pieces with low electric power and hence, such a piezoelectric vibrator constitutes a piezoelectric vibrator which exhibits high energy efficiency.
As one of general methods which suppress an equivalent resistance value, as shown in FIG. 21 and FIG. 22, there has been known a method where the inside of the cavity C in which the piezoelectric vibrating piece 203 is sealed is brought into an almost vacuum state thus lowering a serial resonance resistance value (RI) which has the proportional relationship with the equivalent resistance value. As a method for bringing the inside of the cavity C into a vacuum, there has been known a method (gettering) which activates a gettering film 220 formed on the vibration arm portion 204 by radiating a laser beam to the gettering film 220 from the outside (see Japanese patent 3998948). The gettering film 220 is formed continuously toward a weight-metal-film-211 side from the excitation electrode 212 using the same material (for example, aluminum) as the excitation electrode 212.